HANOI, Vietnam — A Chinese survey vessel has re-entered disputed waters in the South China Sea, according to ship tracking analysis, after a tense month-long standoff in the same area that inflamed tensions between Hanoi and Beijing.

China has been accused of deploying warships, arming outposts and ramming fishing vessels in the waters, stoking ire from other claimants on the key global shipping route.

Hanoi said last week the ship had left the area, but on Tuesday it had returned, according to the US-based Center for Advanced Defense Studies (C4ADS).

The ship was accompanied by at least two Chinese coast guard ships, and several Vietnamese ships closely followed the Chinese fleet.

It remained in the area early Wednesday, C4ADS senior analyst Devin Thorne said.

He said the survey ship's operations in the area "reflect China's purposeful use of civilian, commercial, scientific and paramilitary resources to pursue its interests in and vision for the South China Sea".

Vietnamese officials did not immediately respond to AFP's request for comment.

The United States lashed out at China for its "bullying behaviour" in the South China Sea after initial reports emerged of the survey ship in what Vietnam says is its exclusive economic zone last month.

US Secretary of State Mike Pompeo in July accused Beijing of "coercion" in the sea and urged South East Asian nations to stand up to the superpower.

Beijing often invokes it so-called nine-dash line to justify its apparent historic rights over most of the South China Sea, parts of which are also claimed by Taiwan, Malaysia, the Philippines and Brunei.

Hanoi and Beijing have long sparred over the area, with tensions coming to a head in 2014 when China moved an oil rig into waters claimed by Vietnam.

China has rejected as “unwelcome” the call of the United Kingdom, France and Germany on the South China Sea claimants to respect the arbitration ruling of 2016 and the rules-based framework laid out in the United Nations Convention on the Law of the Sea (UNCLOS).

The Philippines and China effectively consigned to limbo on Thursday the UNCLOS-based arbitral ruling in 2016 on their maritime disputes, and moved to explore instead a wider Code of Conduct for resolving conflicts in the South China Sea.

It would be a betrayal of public trust should the Duterte administration accept China’s rejection of the landmark ruling that invalidated its sweeping claim over the South China Sea, parts of which is the West Philippine Sea, former Foreign Affairs Secretary Albert Del Rosario said Saturday.